1. Field of the Invention
The present invention relates generally to a specialized type of wheel utilized in devices designed for climbing stairs and, more particularly, to a novel configuration for such a wheel incorporating a plurality of involute curves into the outer surface of the wheel to allow a substantially sxooth ascent or descent of stairs.
2. Description of the Prior Art
There is and has been a substantial problem in moving a load too heavy to merely carry up a flight of stairs. The most popular approach has been to use a dolly having conventional round wheels to carry a load up the stairs. However, by using a dolly, the flight of stairs must be ascended one step at a time, by lifting the load up the rise of each step and then rolling it back on the tread of the step to the edge of the next step, and repeating the process until the load is at the top of the stairs. The conventional round wheel has substantial utility in a dolly despite the tedious effort required, but it has not been possible to use the basic round wheel in many applications more complex than the simple dolly.
The next step forward in the art has been demonstrated in a substantial number of patents, and involves modifying the wheel by providing a mounting arrangement allowing multiple wheels to be mounted on a revolving hub to allow the smaller multiple wheels to be levered around the edge of a step. Specific examples of this configuration may be found in U.S. Pat. Nos. 2,742,973, 3,326,563, and 3,515,401, which are representative of a large number of such patents in the United States and abroad. For some reason this technique has found particular application in wheelchairs, although such wheelchairs are thought to be rather risky and not very practical.
While these devices do present some advantage over the basic simple wheel, without exception they have tremendous disadvantage with respect to the non-linear path traveled by the center line of the axle connecting the wheel assemblies to the devices, as well as the loads carried by the devices. The old saying that the shortest distance between two points is a straight line is particularly true when moving loads up or down stairs, and unfortunately a straight line is not available in the operation of the devices using the multiple wheel configuration described above.
As the multiple wheels in such devices swivel about the mounting hubs, the central point of the mounting hubs moves at times in a horizontal direction and at times in a vertical direction, but rarely in a direction paralleling the ascent of the stairs. The advantage resulting from the multiple wheel configurations is twofold: first, the principle of the lever is used to climb to the next highest stair and, second, optional ratcheting mechanisms in some references resist hub movements characterizing a downward movement of the device. While these advantages probably offset the higher construction cost of the devices in some cases, the additional cost is bound to be a negative factor, particularly in combination with the substantial disadvantage of not being able to move loads in a straight line on stairs.
It is therefore apparent that it would be desirable to have a wheel for use with a variety of devices to enable movement of the devices up and down stairs in a substantially straight line, rather than bumping up or down the individual stairs. Such a wheel should function to move up stairs with the hub or mounting point moving in an uninterrupted fashion without requiring any external mechanization to move the wheel The wheel should be constructed in one piece as far as possible to minimize the cost of construction.
It is desirable that the wheel be adaptable to use with any of the plurality of devices which may be operated on stairs. The wheel should also have a high quality of construction to make it durable and long lasting as well as inexpensive. Finally, the wheel should present all of these advantages without substantial disadvantage.